Suppose a bicycle was coasting on a level surface, and there was no friction. what would happen to the bicycle? a. it would speed up since there is no friction. b. it would slow down until it finally came to a stop. c. it would slow down but would never stop. d. it would keep going at constant speed.

You exhale co2 which is produced during cellular respiration.  co2 combines with the water in your blood's plasma to make up one half of the body's most important buffer pair, carbonic acid.  the more physical activity you engage in, the more co2 your body is producing.  you can see this by putting some of the cabbage indicator in a glass and then blowing bubbles into it through a straw.  can you see a change in the color of the indicator?